1. Field of the Invention
The invention relates to an alarm system for detecting movement or change in the field of view supervised by a television camera.
2. Description of the Prior Art
Television-based alarm systems are known in which a value, dependent upon the picture content of the video signal produced by the television camera, is stored and compared with a value derived at a later time so as to produce a difference, and in which an alarm is emitted upon the difference so produced being in excess of a certain threshold value.
Such a system is disclosed in DT-OS No. 19 13 768. In this system, for the purpose of detecting relevant variations, the total field under supervision is subdivided into a number of individual regions which are separately evaluated. The threshold value of one region can be adjusted independently from that of the other regions. Thus those regions in which irrelevant background movements take place can be isolated from those where the background remains constant. In this way it is possible to detect slight but relevant variations in the total field under supervision without increasing the probability of a spurious alarm being released.
An object of the present invention is to provide an alarm system for detecting movement or change in the field of view supervised by a television camera and which has, or may be designed to have, an increased reliability of response to relevant variations in the total supervised field and at the same time a reduced probability of the release of spurious alarms caused by unavoidable disturbances of a stochastic character. A further object is to provide a system which can be implemented at a reduced capital cost as compared with the prior art.